In general, an injection-molding machine for molding a plastic product is an apparatus for injecting a resin raw material into a manifold from a resin-melted mold clamping cylinder, evenly distributing the injected resin along a resin flow path branched within the manifold to be supplied to each of one or more nozzles combined at a lower portion of the manifold, and then injecting the resin into a molding space formed by upper and lower molds, which are product molding frames, that is, a cavity. The injection-molding machine is configured to open/close a gate, that is, an exit, by an elevating operation of a valve pin, and in a case where relatively several articles are molded at the same time according to the number of molded articles, a manifold type of injection-molding machine receiving the resin through the manifold is used, and in a case where a single article is produced, a single type of injection-molding machine is used.
FIG. 1 is a cross-sectional diagram schematically illustrating a hot runner system for an injection-molding machine elevating a valve pin by using high-pressure air as an operation pressure in the related art. As illustrated in FIG. 1, a valve apparatus for an injection-molding machine for a mold having multi cavities in the related art generally includes a driving unit 100 and a valve apparatus 200, and uses high-pressure air as a driving source for an elevating operation of the valve pin 210. That is, the driving unit 100 is provided with a plurality of air channels 110 and 120, which are pipes for supplying high-pressure air from the outside and discharging high-pressure air to the outside, and has a structure in which a piston 140 within a cylinder housing 130 is elevated by the high-pressure air selectively introduced through the plurality of air channels 110 and 120. In this case, a valve pin 210 is connected with a lower end of the piston chamber 130 to interwork with the piston head 140. Further, the valve pin 210 is elevated through the interworking with the piston 130 to selectively close or open a gate, that is, an exit, forming a leading end of a nozzle 220.
In the meantime, the valve apparatus 200 forms an outer body, and includes a nozzle 220, around which a heater for preventing the resin from being solidified is wound, and has a structure in which the valve pin 210 is installed to be vertically elevated inside the nozzle 220. Here, the nozzle 220 is provided with a resin channel 230 while having a predetermined gap around the valve pin 210, and both ends of the resin channel 230 are connected to an exit of the nozzle and the resin channel 310 of the manifold 300, respectively.
In the valve apparatus for the injection-molding machine for the mold with the multi cavities configured as described above, when a high operation pressure is selectively supplied through the air channels 110 and 120, the piston 140 is raised or lowered, and the valve pin 210 simultaneously interworks with the piston 140, so that an elevating operation is integrally performed. Accordingly, the exit of the nozzle is opened or closed according to the elevation of the piston 140, and as a result, the resin supplied through the manifold 300 is supplied into the mold through the exit, or is blocked.
Briefly, the valve gate (exit) apparatus for the injection-molding machine operated having the air pressure as the operational resource in the related art selectively supplies high-pressure air inside the cylinder housing 130 through the corresponding air channels 110 and 120, to elevate the piston head 140, and in this case, the valve pin 210 interworks with the piston head 140 to open/close the exit (gate) of the nozzle.
However, the valve apparatus according to the related art having the aforementioned configuration uses high-pressure air as an operation source for raising the valve pin, and thus needs to adopt a sealing structure for preventing air from being discharged, and requires a large pneumatic device (compressor) for supplying an operational pressure, so that a volume thereof is increased and thus a structure thereof becomes complex, thereby having disadvantages of many limits in an installation space and extremely poor maintenance and management.
Further, in a case where the valve apparatus is applied to the mold having multi cavities including several nozzles, a deviation is generated in the amount of injection of each nozzle due to a size distribution of each nozzle, so that there is difficulty in mass production of molded articles having a uniform quality.
In order to solve the problem, the applicant obtains the registration of the utility models for a valve apparatus for vertically operating a valve pin by power through Korean Utility Model Application No. 2002-09883 (Registration No. 0280604, decided to be granted), Korean Utility Model Application No. 2002-09884 (Registration No. 0280605, decided to maintain the registration), Korean Utility Model Application No. 2002-09885 (Registration No. 0280606, decided to maintain the registration, Korean Utility Model Application No. 2002-19175 (Registration No. 0290456, decided to maintain the registration), Korean Utility Model Application No. 2003-0034932 (Registration No. 0341515, decided to maintain the registration), and Korean Utility Model Application No. 2003-0038360 (Registration No. 0344137, decided to maintain the registration). In schematically reviewing a configuration of the valve apparatus, the valve apparatus generally includes a nozzle and a driving means, and in this case, has a general valve structure in which the nozzle is provided with a resin flow path for receiving a resin therein and injecting the received resin into a mold through an exit provided at a front end portion. Further, a normal reversible motor or a solenoid actuator for raising and lowering the valve pin by a supply of power is used as the driving means. The aforementioned valve apparatus filed in advance by the present applicant may reduce a size of the general valve apparatus by the structure adopting the normal reversible motor or the actuator driven through the supply of the power as the driving source, so that it is possible to increase a degree of freedom in designing the mold and to rapidly and accurately control the amount of movement of the valve pin.
However, in a case where the normal reversible motor serves as the driving source, several valve apparatuses filed in advance by the present applicant need to include a decelerator, and also need to adopt a cooling structure for cooling the motor, so that several valve apparatuses have complex structures, thereby causing difficulty in economically manufacturing the valve apparatuses.
In the meantime, in a case of the actuator using a solenoid principle, it is possible to relatively simplify a structure, but there is a disadvantage in that driving is not smoothly performed at a time at which the valve pin moves to a relative position in a state where the exit is opened or closed. This is not a phenomenon generated only in the solenoid actuator. The valve pins in almost all of the hot runner systems have a state in which ends thereof are fitted to the exit and the other end thereof is fitted to a bushing supporting the valve pins so as to allow a straight motion when closing the exit (gate). In a case where the valve pin is elevated in order to open the exit in this state, power, that is, large power, sufficient to overcome stop resistance applied to the valve pin (frictional resistance due to a support element, such as the bushing supporting the valve pin and the like, and frictional resistance applied when the valve pin is fitted to the exit) is required. That is, in most of the hot runner systems, a driving source with an output higher than a rated output is applied in order to overcome frictional resistance applied at an initial state when the valve pin moves to the relative position in a state where the valve pin is raised or lowered, and perform the lowering or raising operation of the valve pin.
Accordingly, the driving source (a hydraulic pneumatic cylinder housing, the normal reversible motor, and the actuator) with a high output is demanded, such that manufacturing cost is increased, and a volume of the valve apparatus is increased, such that a degree of application freedom for a mold for molding a small and precise injection-molding article is considerably limited. Especially, in a case where a small and precise component is molded, or a product is molded by using a resin containing glass fiber or a magnesium ingredient having poor flowability, there is a problem in that the valve pin is not smoothly elevated.
Further, an end portion of the nozzle is in contact with the mold, so that heat of the nozzle is lost to the mold, and when the resin flows, the resin maintains a melted state by a heater wound around an exterior surface of the nozzle, but when the flow of the resin is stopped, the resin at the end portion of the nozzle is solidified due to heat loss generated at the end portion of the nozzle, and thus an injection process needs to be temporarily stopped until the solidified resin is melted again, thereby degrading production capability and generating poor molding in a case where the solidified resin is not completely melted.
In order to solve the problem, a heating means using a high frequency or a low pressure method is additionally mounted in order to rapidly heat the end portion of the nozzle in the related art, however, the mold, which is in contact with the end portion of the nozzle, is damaged due to the rapid heating of the end portion of the nozzle, thereby leading to a severe problem of shortening a lifespan of the mold. Further, the heating means using the high frequency and the low pressure method is installed around the nozzle, so that the entire volume of the valve apparatus is increased, and thus the degree of design freedom is restricted, and it is impossible to apply the heating means by the high frequency and the low pressure method to the mold for manufacturing a small and precise molded article, a structure of the heating means becomes complex, so that it is difficult to maintain and manage the heating means, and high-priced high frequency and low pressure equipment needs to be additionally installed, so that economic feasibility is decreased.